Miniature indicating fuse



March 7, 1967 J. E. THOMPSON 3,308,257

MINIATURE INDICATING FUSE Filed Oct. 23, 1965 2 Sheets-Sheet 1 lNVENTOR J. E. THOMPSON AT TORNE V March 7, 1967 E. THOMPSON 3,308,257

MINIATURE INDI CAT ING FUSE Filed Oct. 23, 1965 2 Sheets-Sheet 2 United States Patent 3,308,257 MINIATURE INDICATING FUSE Joel E. Thompson, Newark, N.J., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed Oct. 23, 1965, Ser. No. 503,182 9 Claims. (Cl. 200-123) This invention relates to electrical fuses and in particular to a novel structural arrangement for a miniature indicating fuse.

In almost all segments of the electronics industry the needs are increasingly acute for ever smaller components and complete electrical systems. Understandably, miniaturization work has concentrated on the critical, high usage circuit elements and as a result a large variety of extremely small components, active and passive, are now routinely employed. Not all circuit elements, however, have been miniaturized successfully, and consequently some type of modules and equipment requiring these elements necessarily have remained bulky. Of the remaining few components which, for one reason or another have defied miniaturization, the simple indicator fuse has presented perhaps the most vexing assortment of problems.

A major impasse in the miniaturization of indicator fuses has been that the reduced-size visual indicator element does not stand out or readily draw attention. A related concern is the mechanical reliability of these fuses, which is sometimes sacrificed with any significant size reduction. Another problem involves the leaf or coil spring normally used to release a warning mechanism of some sort when the fuse blows. These springs are rather expensive and in the smaller sizes tend to be delicate.

Accordingly, an object of the invention is to reduce substantially the size, bulk and weight of indicator fuses.

Another object of the invention is to increase the reliability of such fuses.

A further object of the invention is to simplify the structure of indicator fuses without decreasing their reliability.

A still further object of the invention is to make the indicator element more easily seen.

These and other objects of the invention are achieved, broadly, by employing as the indicator element a resilient strip such as nylon or other plastic that springs erect from a position of confinement in which it is held in restraint by the fusing element until the latter burns out.

In accordance-with one embodiment of the invention, the body of the indicator fuse comprises a thin mounting board with opposed electrical terminals on the sides and a tab extending up from one end of the board. The tab serves as a finger grip for the fuse; and its inner edge and the adjacent topedge of the board provide a seat for the indicatorelement. This element is produced as an elongated, narrow and normally straight strip. One end of the strip is rigidly supported on a selected surface of the board that is situated substantially in the plane which the strip is to occupy when in the indicating position. This surface may be one opposite the tab base in which case, to impart a spring tension to the strip, the latter is bent down flush against the top edge of the board and the tab inner edge. The strip is retained in this position by the fusing element connected across the top edge between the fuse terminals. Pursuant to the invention, when a current overload causes burn-out of the fuse element, the strip is released and springs erect, well above and away from the tab.

The manner of supporting the strips end on the fuse body may be varied to suit specific considerations of cost and design. For example, the indicator strip may comprise the center leg of a flat T, the outer legs of which are secured against respective sides of the body and in turn support the crosspoint of the T in the desired plane. Alternatively, the indicator element may be an extension leg of a resilient, closed loop that stretches around the fuse body and holds the leg in the desired position. Further methods for supporting the indicator are described below.

In accordance with another aspect of the invention, the indicator strips may be made in various specific colors, each color denoting, for example, a separate type of circuit, a separate current or voltage rating, or some other fact of significance.

In accordance with a further aspect of the invention, the indicator strip may be so retained on the fuse body that a surface of the strip is connected until the fuse element burns out. A suitable radiant energy-sensitive coating may be applied to this surface so that when the element springs erect and exposes same, the presence of the chosen energy will cause the element to glow. Burnout of this fuse, even in a large grouping, can be detected visually almost at once.

Accordingly, a feature of the invention resides in the use of a narrow resilient strip such as nylon or other plastic, as the indicator element of an indicating fuse.

A further feature of the invention relates to the retention by the fusing element itself of an indicator strip in a position of restraint along an edge of the fuse body until overload occurs.

A further feature of the invention lies in a fuse indicator strip formed of material that is both resilient and producible in numerous colors.

These and other objects and features of the invention are described in greater detail in the following illustrative embodiments thereof and in the drawing in which:

FIGS. 1A and 1B are perspective views of two possible embodiments of the indicator element;

FIG. 2 is a perspective view of an indicator element mounted on a fuse;

FIG. 3 is a perspective view of several such fuses in a fuse block;

FIG. 4 is a perspective view of an alternative indicator element;

FIG. 5 is a perspective view of an alternative fuse body;

FIGS. 6 and 7 are perspective views of two further variations of the indicator element; and

FIGS. 8 and 9 are perspective views of an additional variation of an indicator element.

FIG. 1A illustrates one embodiment of the novel indicator element. A unitary element 10 is shown comprising a center leg 11, a left leg 12 and a right leg 13. Advantageously, element 10 is formed in the shape of a flat T as shown in FIG. 1, of a relatively resilient springy electrically insulating material such as nylon, polysulfone or polyvinylchloride. In this embodiment, center leg 11 functions as the indicator in a manner to be described, while legs '12 and 13 are supportive.

FIG. 2 shows a complete indicator fuse, designated as 20, with element 10 installed and retained in its nonindicating mode. Fuse 20 comprises a slim nonconductive mounting board or body 21, wafer-like in shape, with electrical contact surfaces'22 and '23 disposed on opposite sides of board 21, a gripping tab 24 formed by an extension of board 21 and a fusing element 25 connected between surfaces 22 and 23. Indicator element 10 is mounted upon board 21 with its crosspoint 14 positioned near the top of a first end thereof, opposite tab 24. Legs 12 and 13 are bent back and retained flush against opposite sides of board 21 by a suitable adhesive. Indicator leg ,11 is defiexed onto top edge 26 of board 21 and the inner edge 27 of tab 24, retained under stress by element 25. A recess 28 in top edge 26 may be employed to good advantage to increase the overall length of indicator leg 11 and to giveit greater springiness.

FIG. 3 illustrates one practical mounting method for the novel indicator fuses. Shown therein is a connector block 30 and several fuses of the kind described above. Block 30 is a connector for mounting a large number of insertable elements. Each fuse 20 is retained in a separate fuse recess 31 between a pair of oppositely disposed spring contacts 32. The indicator leg 11 of one of the fuses is shown in the erect, indicating position pursuant to the invention, just after its fusing element 25 has burned out. Leg 11 reverts to this, its normal, position due to the bending moment produced at the crosspoint 14 during its mounting on fuse body 20. Indicator leg 11 affords a very clear identification of the blown fuse, since it stands away from and above board 21.

FIG. 1B shows an alternative indicator element structure in which the element, designated 15, comprises a resilient loop 16, a leg 17, and a juncture 18 between leg and loop, formed of the same material as suggested above for element 10. Element 15 is installed on a fuse such as fuse 20 by stretching loop 16 over body 21 so that juncture 18 is situated in the same position on body 21 as the crosspoint of element 10, shown in FIG. 2.

Pursuant to another aspect of the invention, element 10 or its varieties to be described may be produced by wellknown processes in various colors at no appreciable added cost. Numerous useful color code schemes become possible as, for example, for identifying fuse amperage ratings to help insure replacement with the correct type fuse. As an alternative, the color coding applied to the indicator element can identify different circuits, or where desired, establish .a range of relative importance for the various fused circuits. 1

Shown in FIG. 4 is another indicator fuse made pursuant to the invention. This fuse, designated as 40, is similar in construction to those shown in FIG. 3, except that the legs 12 and 13 shown in FIG. 1 have been omitted. In this embodiment the indicator element comprises a single leg 41 with a lower portion 42 that is secured to the front edge 29 of mounting board 21. One method of securing lower portion 42 is with a tabular extension 43 of electrical contact surface 22. Another securing method involves cementing lower leg portion 42 to front edge 29 with a bonding adhesive such as epoxy.

FIG. illustrates a further embodiment of the invention in which the tab 24 of body 21 is reduced in height to conserve space. The indicator element 41 is of the same configuration as shown in FIG. 4, and the mounting thereof upon body 21 is also the same. So that the indicator leg will reach as high in its erect position as occurs in the above embodiments, the top edge 26 of body 21 may be raised to the height of tab 24.

FIG. 6 illustrates a further variation of the inventive concept, featuring here a mounting board 21 in which the recess, for example, element 28 of FIG. 2, has been eliminated. The indicator element 41, which here is substantially the same as that shown in FIG. 4, is doubled over upon itself and retained under stress by the usual fuse element 25. A tab designated as 44 is included as part of body 21, but has a thin shank section 45 to allow more room for seating of the indicator 41 in the position shown. This arrangement has the advantage that less of the indicator 41 is actually in contact with the body 21. Accordingly, the possibility of ambient operating conditions causing indicator 41 to become stuck to body 21 is lessened.

A variation of the inventive concept illustrated in FIG. 6 is depicted in FIG. 7, in which the fuse structure includes an indicator element 41 that is doubled over upon itself several times. In accordance with this aspect of the invention, this structure enables the length of the fuse to be decreased while still achieving the advantages of the structure shown in FIG. 6. By retaining indicator 41 in a pile-up instead of in a single-fold, the same length of indicator may be situated on a smaller seat. Hence, the zlength 47 of the FIG. 7 fuse can be less than the corresponding length 46 of the FIG. 6 fuse without forfeiting any indicator length. The structure shown in FIG. 7 may offer benefits when space is especially-tight.

FIGS. 8 and 9 illustrate a further variation of the invention, both in body structure and importantly in the positioning of indicator element 61. As shown in FIG. 8, a fuse body 51 includes a pair of contact surfaces 52, 53 and a tab extension 54. Indicator element 61 includes a lower portion 63 that is cemented or otherwise afiixed to the inner edge 64 of tab 54 and an upper portion 62. A fusing element 55 connects contact surfaces 52 and 53, and holds element 61 in the nonindicating position by impinging upon a distended end portion 65 of element 61.

When element 55 burns out, the end portion 65 of indicator element 61 is released. The stresses in element 61, produced when leg 62 was doubled over upon lower portion 63 during mounting, cause leg 62 to stand erect. FIG. 9 portrays indicator element 61 in its indicating position. A further advantage is derived by shaping end portion 65 in the form of a nub that can be seen even more readily than the element itself. Of course, the nub structure may be used also in any of the indicator element embodiments already described.

In accordance with an important aspect of the invention, a further improvement in the indicating capabilities of the fuse may be achieved by coating the entire surface 66 of element 61 with some type of radiant energy-sensitive material. coated with a material such as a fluorescent dye that is sensitive to ultra-violet light. One such dye is Calcofluor yellow, made by American Cyanamid Company. An alternative coating is zinc sulfide that is sensitive to infrared light. A third possible coating, known in the trade as Violite, is suitable with ultra-violet light. As long as element 61 is in the nonindicating position shown in FIG. 8, the surface 66 will be hidden. However, when the fuse blows and element 61 springs erect, the entire surface 66 will become visible. By coating surface 66 as described, it is possible to identify very quickly the location of a blown fuse even in a grouping of thousands of fuses, simply by playing the appropriate light into the fuse compartment. Thus, the darkness normally engulfing most fuse compartments and hampering spotting in effect is turned to advantage pursuant to this aspect of the invention.

Various other modifications may be made by persons skilled in the art to the embodiments described, without departing from the spirit and scope of this invention; and it is to be understood expressly that all such modifications fall within the contemplation of the claims to follow.

What is claimed is:

1. An electrical fuse comprising a body with an end tab extending from the top edge thereof and a pair of.electrical contacts with a fusing element therebetween, and means for indicating a burn-out of said fusing element comprising an elongated resilient member having a normally linear shape when under no stress, said member comprising an indicator element, means attaching an end of said member to an edge of said body remote from said' tab, and means including said fusing element securing the remainder of said indicator element in a distended position flush with the inner edge of said tab and also the adjacent upper edge of said fuse body, said fusing element releasing said indicator element .upon burn-out, whereby said indicator element springs erect to signal a blown fuse.

2. An electrical fuse comprising a slim body with an end tab extending from the top edge thereof, a pair of electrical contacts mounted on said body with a fusing element connected therebetween, and means for indicating a burn-out of said fusing element comprising an elongated resilient member having a normally straight shape when For example, surface 66 may be thinly under no stress, means attaching an end of said member to an edge of said body, and means including said fusing element for securing the remainder of said resilient member in a constrained position upon said fuse body top edge, said indicator element being bent back upon itself at least once, said fusing element releasing said indicator element upon burn-out, whereby said indicator element springs erect to signal a blown fuse.

3. An electrical fuse comprising a slim body with an end tab extending tfirom the top edge thereof, a pair of electrical contacts mounted on said body with a fusing element connected therebetween, and means for indicating a burn-out of said fusing element comprising an elongated resilient member having a normally linear shape when under no stress, means attaching a first end of said member opposite the inner edge of said tab, and means including said fusing element securing the second end of said resilient member in a position adjacent said first end thereby to create a bending moment in said element, said fusing element releasing said second end upon burn-out, whereby said indicator element springs erect to signal a blown fuse.

4. An indicator fuse in accordance with claim 1 Wherein said second end of said resilient member further comprises a nub, said fusing element securing said nub thereby to maintain said bending moment in said member until burn-out.

5. An electrical fuse comprising a fiat, relatively slim body with a protruding tab extension at an end of its top edge, a pair of electrical contacts mounted on said body with a fusing element connected therebetween, and means for indicating a burn-out of said fusing element comprising a three-legged resilient member having a normally flat shape when under no stress, means securing two adjacent legs of said member against respective sidesof said fuse body, means including said fusing element securing under stress the third leg against the top edge of said body and the adjacent inner edge of said tab, whereby when said fusing element burns out said third leg is released and springs erect, thereby to signal a blown fuse.

6. An electrical fusing system comprising a wafer-like body including electrical terminals mounted on opposite sides thereof and a top edge thereto, a fusing element ex- 6 tended over said top edge and connected between said terminals, an elongated resilient strip, means mounted on said body including a first end of said strip for supporting said strip on said body in an upright position with respect to said top edge thereby defining an indicating mode, a selected surface of said strip being exposed in said mode, said surface comprising a coating of radiant energy-sensitive material, means including said fusing element for deflexing said strip to a restrainted position defining a nonin- 'dicating mode, said selected surf-ace being concealed in said mode, and means for applying said radiant energy to said fuse, said fusing element releasing said strip upon burn-out, whereby said strip springs upright exposing said coated surface to said radiant energy, said strip glowing in response thereto, to signal a burned fuse.

7. A fuse in accordance with claim 6 wherein said radiant energy-sensitive material comprises a fluorescent dye and said radiant energy comprises ultraviolet light.

8. A fuse in accordance with claim 6 wherein said radiant energy-sensitive material comprises zinc sulfide and said radiant energy comprises infra-red light.

9. A fuse in accordance with claim 6 wherein the color of said resilient means is selected in accordance with a predetermined color coding scheme, each color denoting a separate, prescribed fact concerning said fuse.

References Cited by the Examiner UNITED STATES PATENTS 745,694 12/1903 Utley et al. 200121 809,982 1/ 1906 Rhoades 200121 1,061,894 5/1913 Baker 200-121 1,520,201 12/ 1924 Nenonen 200121 FOREIGN PATENTS 2,353 1/ 1909 Great Britain.

References Cited by the Applicant UNITED STATES PATENTS 2,086,406 7/ 1937 Dieffenbacher.

BERNARD A. GlLHEANY, Primary Examiner.

G SQ A an E am ner. 

1. AN ELECTRICAL FUSE COMPRISING A BODY WITH AN END TAB EXTENDING FROM THE TOP EDGE THEREOF AND A PAIR OF ELECTRICAL CONTACTS WITH A FUSING ELEMENT THEREBETWEEN, AND MEANS FOR INDICATING A BURN-OUT OF SAID FUSING ELEMENT COMPRISING AN ELONGATED RESILIENT MEMBER HAVING A NORMALLY LINEAR SHAPE WHEN UNDER NO STRESS, SAID MEMBER COMPRISING AN INDICATOR ELEMENT, MEANS ATTACHING AN END OF SAID MEMBER TO AN EDGE OF SAID BODY REMOTE FROM SAID TAB, AND MEANS INCLUDING SAID FUSING ELEMENT SECURING THE REMAINDER OF SAID INDICATOR ELEMENT IN A DISTENDED POSITION FLUSH WITH THE INNER EDGE OF SAID TAB AND ALSO THE ADJACENT UPPER EDGE OF SAID FUSE BODY, SAID FUSING ELEMENT RELEASING SAID INDICATOR ELEMENT UPON BURN-OUT, WHEREBY SAID INDICATOR ELEMENT SPRINGS ERECT TO SIGNAL A BLOWN FUSE. 